It is folly for the governments of Mr. Rajapaksa in Sri Lanka, President Thein Sein of Myanmar and Prime Minister Narendra Modi in India, or their political allies, to give even the appearance of tolerating these Islamophobic groups in a region that has too often been convulsed by religious sectarian violence. They should condemn this mad alliance before it can spread further.

On his 79th birthday in July, the Dalai Lama appealed to Buddhist extremist groups in Myanmar and Sri Lanka to stop instigating attacks against Muslim minorities that have killed scores. Instead, in an affront to Buddhism’s core message of compassion, leaders of those groups announced an alliance to make common cause against Muslims.

“The time has come to ally internationally,” Galagodaththe Gnanasara, the leader of the radical Sri Lankan Buddhist group Bodu Bala Sena, announced at a convention held in Colombo last month. The guest of honor was Ashin Wirathu, a Buddhist radical whose picture Time magazine put on its July 1 cover as “The Face of Buddhist Terror.” The government of Prime Minister Mahinda Rajapaksa ignored pleas by Sri Lankan Muslim and Christian civil groups, fearful of more anti-Muslim violence in their country, to deny Mr. Wirathu a visa. Granting Mr. Wirathu a visa can only reinforce the fears of many Muslims that the government — and perhaps more powerful regional allies — back Bodu Bala Sena, which translates as Buddhist Power Force.

Last week, Mr. Gnanasara claimed he was in discussions “at a high level” with the right-wing Indian Hindu group Rashtriya Swayam Sevak to form what he called a “Hindu-Buddhist peace zone” in South Asia. A Rashtriya Swayam Sevak spokesman, Ram Madhav, promptly denied that there were any such discussions. But Mr. Madhav, now general secretary of India’s governing Bharatiya Janata Party, has written comments sympathetic to Bodu Bala Sena and Mr. Wirathu’s group 969 in Myanmar on his Facebook and Twitter accounts.

It is folly for the governments of Mr. Rajapaksa in Sri Lanka, President Thein Sein of Myanmar and Prime Minister Narendra Modi in India, or their political allies, to give even the appearance of tolerating these Islamophobic groups in a region that has too often been convulsed by religious sectarian violence. They should condemn this mad alliance before it can spread further.